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          https://crocs.fi.muni.cz  @CRoCS_MUNI
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PV204 Security technologies
Authentication: passwords, OTP, FIDO U2F
Petr Švenda        svenda@fi.muni.cz        @rngsec
Centre for Research on Cryptography and Security, Masaryk University
Please report any inaccuracies or suggestions for improvements here:
https://drive.google.com/file/d/1WNMU4fmG7sMMcuHHA-jgXQgG2nWkUCoJ/view?usp=sharing
A picture containing text, person, wall, indoor Description automatically generated
IS,1998
2021

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
•
2
PV204 Authentication and passwords
Graphical user interface, text, chat or text message Description automatically generated
•Place/upvote questions in slido while listening to lecture video
•We will together discuss these during every week lecture Q&A

#pv204_2022
#pv204_2024

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COURSE TRIVIA: PV204_00_COURSEOVERVIEW_2024.PDF
•
PV204 Authentication and passwords
3

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Basic terms
•Identification
–Establish what the (previously unknown) entity is
•Authentication
–Verify if entity is really what it claims to be
•Authorization (access control)
–Define an access policy to use specified resource
–Check if entity is allowed (authorized) to use resource
•Authentication may be required before an entity allowed to use resource to which is authorized
PV204 Authentication and passwords
4

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Options for authentication
•Something you:
1.Know (password, key)
2.Have (token, smartcard)
3.Are (biometrics)
•Combination of multiple options – two-factor authentication (or more)
•
1.Registration phase (how is new user added)
2.Verification phase (how is user’s claimed identity verified)
3.Recovery phase (what if user forgot/lost authentication credentials)
5
PV204 Authentication and passwords

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
PASSWORDS
•
PV204 Authentication and passwords
6

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Mode of usage for passwords
•Verify by direct match (provided_password == expected_password?)
–Example: HTTP basic access authentication
–Be aware of plaintext storage on server
–Be aware of potential side-channels (mismatch on Xth character)
•Verify by match of derived value (hash(password | salt))
–Be aware of rainbow tables and brute-force crackers
•Derive key: Password ® cryptographic key
–Example: key = PBKDF2(password)
•Used to establish authenticated key
–Example: Password + Diffie-Hellman ® authenticated key…
7
PV204 Authentication and passwords

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Problems associated with passwords
•How to create strong password?
•How to use password securely?
•How to store password securely?
•Same value is used for the long time (exposure)
•Value of password is independent from the target operation (e.g., authorization of bank transfer
request)
•User usually can’t memorize long-enough password
•…
8
PV204 Authentication and passwords

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Where the passwords can be compromised?
1.Client side (malware on user computer)
2.Database storage
–Cleartext storage
–Backup data (“tapes”)
–Server compromise, misconfiguration
3.Host machine (memory, history, cache)
4.Network transmission (network sniffer, proxy logs)
5.Hardcoded secrets (inside app binary)
•Difficult to detect compromise and change after the exposure
•
PV204 Authentication and passwords
9

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
https://haveibeenpwned.com/ (Troy Hunt)
10
PV204 Authentication and passwords
Total pwned accounts: 12,463,965,246
Collection #1: 772,904,991 accounts!

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
https://haveibeenpwned.com/Passwords
•Check how many times was given password found in leaked datasets
11
PV204 Authentication and passwords
Textové pole: password
password

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Password “hardening” ideas
1.Hash password by one-way function (shall be hard to invert)
2.Slowdown cracking attempts (less potential passwords tried)
3.Enable users to have long, random and unique passwords
4.Have unique password for every authentication attempt
5.Replace/complement passwords with something else (e.g., smartcard)
6.Bind response to server domain name (to prevent phishing)
•
•
•
•
•
12
PV204 Authentication and passwords
In follow-up slides, we will discuss these ideas one by one

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
IDEA: HASH PASSWORDS
•
13
PV204 Authentication and passwords

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
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PV204 Authentication and passwords
Joe; insecure

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
(Hashed-)Password cracking
•Scenario: dump of database with password hashes, find original password
•Password cracking attacks
–Brute-force attack (up to 8 characters)
–Dictionary attack (passwords with higher probability tried first)
–Patterns: Dictionary + brute-force (Password[0-9]*)
–Rainbow tables (time-memory trade-off)
–Parallelization (many parallel cores)
–GPU/FPGA/ASIC speedup of cracking
•Tools
–Generic: Hashcat, John the Ripper, Brutus, RainbowCrack…
–Targeted to application: TrueCrack, Aircrack-NG…
PV204 Authentication and passwords
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D:\Documents\Obrázky\is2\johntheripper1_10_design.png A black and white sign Description
automatically generated with medium confidence

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
D:\Documents\Obrázky\is2\mothermaidens.png
Password reality (from many breaches + pwd cracking)
•User has usually weak password
–>60% were (dictionary) brute-forced
•Server/service is frequently compromised
–Server-side compromises are now very frequent
•Users do not use unique passwords between services
–Gawker and root.com leaks: 76% had the exact same password
•Different authentication channels may not be independent
–Web-browsing + SMS on smart phones?
•Account recovery is often easier to guess than original password
•
•
•
•
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PV204 Authentication and passwords
D:\Documents\Obrázky\is2\johntheripper1_10_design.png
Total pwned accounts: 12,463,965,246
Collection #1: 772,904,991 accounts!

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Insecure password handling … what is the attack?
•Verify by direct match (provided_password == expected_password?)
–Attack: compromise plain passwords on server
•pwdTagi = SHA-2(“password”)
–Same passwords from multiple users => same resulting pwdTag
–Attack: Large pre-computed “rainbow” tables allow for very quick check common passwords
•pwdTagi = SHA-2(“password” | salt)
–Use of rainbow tables “prevented” by addition of random (and potentially public) salt
–Attack: dictionary-based brute-force still possible
•pwdTagi = AES(“password”, secret_key)
–Attack: If secret_key is leaked => direct decryption of all stored pwdTags => passwords
–
PV204 Authentication and passwords
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Some issues addressed by PAKE (Password Authenticated Key Exchange) protocols – future lecture

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IDEA: SLOWDOWN CRACKING ATTEMPTS
•
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PV204 Authentication and passwords

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
D:\Documents\Obrazky\pbkdf2-5002.png
Derivation of secrets from passwords
•PBKDF2 function, widely used
–Password is key for HMAC
–Salt added
–Many iterations to slow derivation
•
•
•Problem with custom-build hardware (GPU, ASIC)
–Repeated iterations not enough to prevent bruteforce
–(or would be too slow on standard CPU – user experience)
•Solution: function which requires large amount of memory
•
PV204 Authentication and passwords
Source: https://nakedsecurity.sophos.com
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          https://crocs.fi.muni.cz  @CRoCS_MUNI
scrypt – memory hard function
•Design as a protection against cracking hardware (usable against PBKDF2)
–GPU, FPGA, ASICs…
–https://github.com/wg/scrypt/blob/master/src/main/java/com/lambdaworks/crypto/SCrypt.java
•Memory-hard function
–Force computation to hold r (parameter) blocks in memory
–Uses PBKDF2 as outer interface
•Improved version: NeoScrypt (uses full Salsa20)
•
PV204 Authentication and passwords
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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Reuse of external PBKDF2 structure
PV204 Authentication and passwords
https://www.reddit.com/r/crypto/comments/3dz285/password_hashing_competition_phc_has_selected/
21

>

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Argon2 – memory hard function
•Password hashing competition (PHC) winner (2013/2020)
–Large (configurable) memory size is required
•Memory hard functions are (slowly) replacing PBKDF2
•Now available in OpenSSL 3.2
•Why it slows down GPU cracking?
–GeForce RTX 4080 X3 16GB (9 728 cores, 16GB)
–GPU has thousands cores => thousands PBKDF2 passwords tested in parallel
–If Argon2 is used with 1GB memory required => max 16 passwords in parallel
•Why not parametrize with 16GB?
–Legitimate user must also have available memory (mobile phone…)
•
PV204 Authentication and passwords
https://www.reddit.com/r/crypto/comments/3dz285/password_hashing_competition_phc_has_selected/
22

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
IDEA: LONG, RANDOM AND UNIQUE PASSWORDS
•
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PV204 Authentication and passwords

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
PASSWORD MANAGERS
•
24
PV204 Authentication and passwords

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Evolution of password (managers)
1.Human memory only
2.
2.Write it down on paper
3.
3.Write it into file
4.
4.Use local password manager
5.
5.
25
PV204 Authentication and passwords
D:\Documents\Obrázky\is2\Body-Brain-icon.png
Pαs$w0rd
Pαs$w0rd01
Google:
Sfdlk2c&
Skype:
*(&21mefd
D:\Documents\Obrázky\is2\NotepadRv1.png devil
Google:
Sfdlk2c&432mo%
Skype:
*(&21mefd872!&
Google:
Sfdlk2c&432mo%
Skype:
*(&21mefd872!&
devil D:\Documents\Obrázky\is2\Key-icon.png D:\Documents\Obrazky\is2\synchronization.png

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
D:\Documents\Obrázky\is2\Plain-Blue-icon.png
Remote password managers
Google:
Sfdlk2c&432mo%
Skype:
*(&21mefd872!&
D:\Documents\Obrázky\is2\Lock-icon.png D:\Documents\Obrázky\is2\Phone-icon.png
D:\Documents\Obrázky\is2\ipad-black-icon.png D:\Documents\Obrázky\is2\Computer_Icon.png
D:\Documents\Obrázky\is2\Key-icon.png D:\Documents\Obrázky\is2\Key-icon.png
D:\Documents\Obrázky\is2\Key-icon.png
KeePass+Dropbox
LastPass
1Password
MozillaSync
Firefox Lockwise
…
PV204 Authentication and passwords
26

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
•
D:\Documents\Obrázky\is2\lastpasshack.png >
But passwords are encrypted, right?
D:\Documents\Obrázky\is2\lastpass_usersshouldbesafe.png
PV204 Authentication and passwords
27

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28
PV204 Authentication and passwords
Graphical user interface, text, application Description automatically generated Graphical user
interface, text, application Description automatically generated

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Devil is in the details
•How are passwords encrypted? (PBKDF2 or Argon2? Parameters?)
•How are legacy users handled? (possible smaller parameters)
•Is everything encrypted? (URL, notes, IPs…)
•Is recovery possible? How?
•
29
PV204 Authentication and passwords

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PASSWORD MANAGER FOR MULTIPLE DEVICES
•Case study
PV204 Authentication and passwords
30

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Functional and security assumptions
•Functional
–User stores fixed secrets (passwords…)
–User has multiple connected devices
–Easy to use J
•Security
–Service can’t be trusted
–User chooses weak password
–Devices can be lost (and later revoked)
–User has independent channel (phone)
•
•
PV204 Authentication and passwords
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Main security design principles
I.Treat storage service as untrusted and perform security sensitive operations on client
II.Make necessary trusted component as small as possible
III.Prevent offline brute-force, but don’t expect strong password from user
–add entropy from other source
IV.Make transmitted sensitive values short-lived
V.(Trusted hardware can provide additional support)
–
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PV204 Authentication and passwords

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
>
Public-key cryptography indirection
D:\Documents\Obrázky\is2\Plain-Blue-icon.png
Google:
Sfdlk2c&432mo%
Skype:
*(&21mefd872!&
D:\Documents\Obrázky\is2\Lock-icon.png D:\Documents\Obrázky\is2\Computer_Icon.png
D:\Documents\Obrázky\is2\Body-Brain-icon.png D:\Documents\Obrázky\is2\Key-icon.png
K = H(‘Password’)
K
D:\Documents\Obrázky\is2\Plain-Blue-icon.png
Google:
Sfdlk2c&432mo%
K
Password
  Priv_U
KEK
  K
Pub_U
D:\Documents\Obrázky\is2\Computer_Icon.png D:\Documents\Obrázky\is2\Body-Brain-icon.png
D:\Documents\Obrázky\is2\Key-icon.png
Password
KEK = H(‘Password’)
PV204 Authentication and passwords
33

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
D:\Documents\Obrázky\is2\Computer_Icon.png D:\Documents\Obrázky\is2\ipad-black-icon.png
D:\Documents\Obrázky\is2\Phone-icon.png >
Public-key crypto indirection
D:\Documents\Obrázky\is2\Plain-Blue-icon.png
Google:
Sfdlk2c&432mo%
K
  Priv_U
KEK
  K
Pub_U
D:\Documents\Obrázky\is2\Computer_Icon.png D:\Documents\Obrázky\is2\Key-icon.png
Password
KEK = H(‘Password’)
>
Public-key crypto indirection allows for asynchronous change of K
>
Long private key can be also stored on Service
D:\Documents\Obrázky\is2\User-Group-icon.png
K’,K’’,K’’’…
[K’]Pub_U
PV204 Authentication and passwords
34

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
>
Weak password?
D:\Documents\Obrázky\is2\Plain-Blue-icon.png D:\Documents\Obrázky\is2\Plain-Blue-icon.png
•
Google:
Sfdlk2c&432mo%
K
  Priv_U
KEK
  K
Pub_U
D:\Documents\Obrázky\is2\Computer_Icon.png D:\Documents\Obrázky\is2\Key-icon.png
Password
KEK = H(‘Password’)
Password
KEK = H(‘Password’)
KEK
Priv_U
K
K
Google:
Sfdlk2c&432mo%
>
Attacker has motivation for attacking the Service!
>
Users tend to have weak passwords…
PV204 Authentication and passwords
35

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
D:\Documents\Obrázky\is2\Home-Server-icon.png D:\Documents\Obrázky\is2\Home-Server-icon.png >
Trusted server/secure element
•
D:\Documents\Obrázky\is2\Plain-Blue-icon.png
Google:
Sfdlk2c&432mo%
K
  Priv_U
KEK
  K
Pub_U
D:\Documents\Obrázky\is2\Computer_Icon.png D:\Documents\Obrázky\is2\Body-Brain-icon.png
D:\Documents\Obrázky\is2\Key-icon.png
Password
KEK = H(‘Password’
D:\Documents\Obrázky\is2\Home-Server-icon.png
User1:SecretData
User2:SecretData’
…
>
Separate trusted entities provide additional data
| SecretData)
devil
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devil >
Larger attack surface on Trusted server (connection from world)

Problems:
- Attacker may compromise SecretData during transit
- Trusted server must accept network connections from whole world => larger attack surface

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•
D:\Documents\Obrázky\is2\Plain-Blue-icon.png
Google:
Sfdlk2c&432mo%
K
  Priv_U
KEK
  K
Pub_U
D:\Documents\Obrázky\is2\Computer_Icon.png D:\Documents\Obrázky\is2\Body-Brain-icon.png
D:\Documents\Obrázky\is2\Key-icon.png
Password
KEK = H(‘Password’ | SecretData)
D:\Documents\Obrázky\is2\Home-Server-icon.png
User1:SecretData
User2:SecretData’
…
D:\Documents\Obrázky\is2\nokia_7.jpg
SMS:
D:\Documents\Obrázky\is2\Key-icon.png
SecretData
D:\Documents\Obrázky\is2\Key-icon.png
SecretData
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>
Multiple devices
•
D:\Documents\Obrázky\is2\Plain-Blue-icon.png
Google:
Sfdlk2c&432mo%
K
  Priv_U
KEK
  K
Pub_U
KEK
Dev1
KEK
Dev2
KEK
Dev3
D:\Documents\Obrázky\is2\Phone-icon.png D:\Documents\Obrázky\is2\ipad-black-icon.png
D:\Documents\Obrázky\is2\Computer_Icon.png
Dev1
Dev2
Dev3
PV204 Authentication and passwords
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Dev1 = H(‘Password1’|SecretData1)

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•
•Device management (new, remove, revoke)
•Device authentication
•Group management (users, boards, secrets)
•Password change, private key change
•Access recovery
•…
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PV204 Authentication and passwords
>
Devil is in the details…
>
Other operations
devil

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Do we have some implementations?
•Apple iCloud Keychain - service showcased in 2013
•Lack of details until iOS Security report 02/2014
–https://web.archive.org/web/20150319073804/https://www.apple.com/business/docs/iOS_Security_Guide.
pdf
–https://blog.cryptographyengineering.com/2016/08/13/is-apples-cloud-key-vault-crypto/ (M.Green)
•Current platform details (Advanced Data Protection for iCloud)
–https://help.apple.com/pdf/security/en_US/apple-platform-security-guide.pdf
–
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PV204 Authentication and passwords

https://support.apple.com/guide/security/icloud-keychain-security-overview-sec1c89c6f3b/1/web/1

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 Apple’s iCloud Keychain
•Multiple similarities to the described example
–Layer of indirection via asymmetric cryptography
–Support for multiple devices
–Asynchronous operations via application tickets
–Authorization and signature of additional devices
–User phone registered and required
•Still reliance on user’s (potentially weak) password for recovery
–But only limited number of tries allowed
•Trusted component via internal HSM (Hardware Security Module)
–Recovery mode with 4-digit code (default, can be set longer)
–HSM will decrypt recovery key only after code validation
–Note: only 4 digits is not an issue here – HSM enforce limited # retries
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IDEA: HAVE UNIQUE PASSWORD FOR EVERY AUTHENTICATION ATTEMPT
ONE-TIME PASSWORDS: HOTP & TOTP
•
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ONE-TIME PASSWORDS
•
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Recall: Problems associated with passwords
•How to create secure password?
•How to use password securely?
•How to store password securely?
•Same value is used for the long time (exposure)
•Value of password is independent from target operation (e.g., authorization of request)
•…
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PV204 Authentication and passwords
One-time passwords tries to address these issues

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HMAC-based One-time Password Algorithm (RFC 4226)
•HMAC-based One-time Password Algorithm (HOTP)
–Secret key K
–Counter (challenge) C
–HMAC(K,C) = SHA1(K ⊕ 0x5c5c… ∥ SHA1(K ⊕ 0x3636… ∥ C))
–HOTP(K,C) = Truncate(HMAC(K,C)) & 0x7FFFFFFF
–0x7FFFFFFF mask to drop most significant bit (portability)
–HOTP-Value = HOTP(K,C) mod 10d     (d … # of digits)
•Many practical implementations
–E.g., Google Authenticator
•https://en.wikipedia.org/wiki/HOTP
•
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HOTP – items, operations
•Logical operations
1.Generate initial state for new user and distribute key
2.Generate HOTP code and update state (user)
3.Verify HOTP code and update state (auth. server)
•Security considerations of HOTP
–Client compromise
–Server compromise
–Repeat of counter/challenge
–Counter mismatch tolerance window
–Phishing – user enters HOTP code at phishing website
•
•
•
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Sylvain Maret
Time-based One-time Password Algorithm
•Very similar to HOTP
–Time used instead of counter
•Requires synchronized clocks
–In practice realized as time window
•Tolerance to gradual desynchronization possible
–Server keeps device’s desynchronization offset
–Updates with every successful login
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OCRA: OATH Challenge-Response Algorithm
•Initiative for Open Authentication (OATH)
•OCRA is authentication algorithm based on HOTP
•OCRA code = CryptoFunction(K, DataInput)
–K: a shared secret key known to both parties
–DataInput: concatenation of the various input data values
•Counter, challenges, H(PIN/Passwd), session info, H(time)
–Default CryptoFunction is HOTP-SHA1-6
–https://tools.ietf.org/html/rfc6287
•Don’t confuse with Oauth (delegation of authentication)
–The OAuth 2.0 Authorization Framework (RFC6749)
–TLS-based security protocol for accessing HTTP service
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>

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Increased risk at *OTP verification server
•More secure against client compromise
–Using OTP instead of passwords, KDF(time|key),
•But what if server is compromised?
–database hacks, temporal attacker presence
–E.g., Heartbleed – dump of OTP keys
•Possible solution
–Trusted hardware on the server
–OTP code verified inside trusted environment
–OTP key never leaves the hardware
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Problems:
1. Is OTP code fresh?
2. Is OTP generated for correct domain (not phishing)?

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Possible password replacements
•Cambridge’s TR – wide range of possibilities listed
–The quest to replace passwords: a framework for comparative evaluation of Web authentication
schemes
–https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-817.pdf
•Many different possibilities, but passwords are cheap to start with, a lot of legacy code exists
and no mechanism offers all benefits
•Mandatory reading: UCAM-CL-817
–At least chapters: II. Benefits, V. Discussion
–Whole report is highly recommended
–
•
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IDEA: REPLACE PASSWORD BY SMARTCARD WITH ASYMMETRIC KEYPAIR, CHALLENGE-RESPONSE PROTOCOL AND
PREVENT PHISHING
•
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FIDO U2F PROTOCOL
(U2F → FIDO2 → WEBAUTHN)
•
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Revision 1: ECC-based challenge-response
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PV204 Authentication and passwords
https://developers.yubico.com/U2F/Protocol_details/Overview.html
>
Problems: phishing, MiTM…
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Revision 2: URI + TLS channel id added
•
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PV204 Authentication and passwords
https://developers.yubico.com/U2F/Protocol_details/Overview.html
>
Problem: using same device => detectable by services (same kpub)
https://accounts.google.com/ServiceLogin
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Revision 3: Application-specific key added
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PV204 Authentication and passwords
https://developers.yubico.com/U2F/Protocol_details/Overview.html
>
Problem: Undetectable device cloning
new key pair and key handle for each registration
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Revision 4: Authentication counter added
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https://developers.yubico.com/U2F/Protocol_details/Overview.html
>
Option: What if server wants to verify device properties before register?
Incremental counter
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Revision 5: Device attestation added
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PV204 Authentication and passwords
https://developers.yubico.com/U2F/Protocol_details/Overview.html
Attestation certificate signed with TTP
•
>
ECDSA NIST secp256r1 used
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FIDO U2F – current state
•FIDO alliance of major companies
•U2F → FIDO2 → WebAuthn (more than “just” U2F)
•Original U2F protocol extended and moved under W3 as WebAuthn
–https://www.w3.org/TR/webauthn/
•Large selection of tokens now available (including open-hardware)
•Android added systematic support for FIDO U2F (02/2019)
–Android phone acts as U2F token
–https://www.wired.com/story/android-passwordless-login-fido2
•Google Smart Lock app on iOS uses secure enclave and acts as FIDO token
•Since iOS 13.3. USB, NFC, and Lightning FIDO2-compliant security keys in Safari browser (12/2019)
–
–
•
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CTAP/WebAuthn stack
•WebAuthn Protocol
–Asymmetric crypto-based challenge-response protocol
–Browser inserts actual URL (origin) as a part of the challenge
–Private key stored and used (token, phone…)
–An API for accessing Public Key Credentials Level 2 (level=version)
•Official documentation: https://www.w3.org/TR/webauthn/
•Client to Authenticator Protocol (CTAP)
–Protocol between browser and authenticator
–Authenticator = initially hardware token, but now range of devices (phones, calculators…)
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https://developers.yubico.com/U2F/Protocol_details/Overview.html
A picture containing drawing Description automatically generated
WebAuthn
Authenticator
             CTAP

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True2F FIDO U2F token
•Yubikey 4 has single master key
–To efficiently derive keypairs for separate Relying parties (Google, GitHub…)
–Inserted during manufacturing phase (what if compromised?)
•Additional SMPC protocols (protection against backdoored token)
–Secure Multi-Party Computation (SMPC) will be covered later
–Verifiable insertion of browser randomness into final keypairs
–Prevention of private key leakage via ECDSA padding
•
•Backward-compatible (Relying party, HW)
•Efficient: 57ms vs. 23ms to authenticate
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https://arxiv.org/pdf/1810.04660.pdf

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WebAuthn - evolution of U2F protocol
•An API for accessing Public Key Credentials Level 2
–Official documentation: https://www.w3.org/TR/webauthn/
–(Level means version here J)
•Similar, but more complex standard than U2F
•Client to Authenticator Protocol (CTAP)
–protocol for communication between browser and token (authenticator)
–USB, NFC, Bluetooth
•CTAP 2.2 adds support for the hybrid transport (FIDO Cross-Device Authentication flow, aka
Passkeys)
•Explanation, demo page https://webauthn.guide/#about-webauthn
•
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Missing piece? “passkeys”
•Authentication on PC with FIDO2 token
•Authentication on mobile phone (with or without token)
•Authentication on PC without FIDO2 token?
•Idea of “passkeys” (multi-device FIDO credentials)
–WebAuthn (“U2F”) protocol used for base authentication (private keys needed)
–Replace hardware token with mobile phone
–Connect mobile phone with PC using Bluetooth LE (BLE) or websockets
•Now supported natively by Apple (Keychain), Google (Password Manager) and Microsoft (Hello)
–https://media.fidoalliance.org/wp-content/uploads/2022/03/How-FIDO-Addresses-a-Full-Range-of-Use-C
ases-March24.pdf
–https://passkeys.dev/docs/reference/specs/
–
–
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FIDO U2F devices
•Why have button? Is missing display problem?
•Existing past attack: direct WebUSB API in Chrome
–Malware bypass U2F API checking the URL
–Legitimate URL is send from malicious page
–https://www.wired.com/story/chrome-yubikey-phishing-webusb/
–APDU-level communication: https://npmccallum.gitlab.io/post/u2f-protocol-overview/
•Well known is Yubikey, but open-source hardware and/or software-only implementations also possible
–https://github.com/conorpp/u2f-zero
–https://github.com/solokeys/solo
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Always dig for implementation details
•How are ECC keys generated and stored?
•Yubikey saves storage memory by deriving ECC private keys from master secret instead of randomly
generating new one
–Possible as the ECC private key is random value
•Device secret generated during manufacturing
•What is the possible attack
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https://developers.yubico.com/U2F/Protocol_details/Key_generation.html

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Summary
•Passwords have multiple issues, but are hard to be replaced
•Major server-side breaches now very common
•Important to use passwords securely (guidelines)
•One-time passwords and tokens getting more used
•Password manager with synchronization over multiple devices is not straightforward, but doable
(e.g., Apple’s iCloud Keychain)
•FIDO2/Webauthn is major authentication improvement – use it!
•Mandatory reading: UCAM-CL-817
–At least chapters: II. Benefits, V. Discussion
–Whole report is highly recommended
•
•
•
•
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•
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Graphical user interface, text, chat or text message Description automatically generated
•
#pv204_2024

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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Hierarchy of authentication and
key establishment goals
PV204 Authentication and passwords
D:\Documents\Obrazky\keystablish_goals.png
Protocols for Authentication and Key Establishment By Colin Boyd, Anish Mathuria
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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Common (mis-)Assumptions
1.User has strong password
2.Server/service is hard to compromise
3.User have unique passwords
4.Different authentication channels are independent
5.Recovery
6.
6.
6.
6.
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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Password cracking defenses
•Don’t transmit or store in plaintext
•Process password on client, transmit only digest
•Don’t encrypt, hash instead
•Use salt to prevent rainbow tables attack
•Use memory-hard KDF algorithms
–To slow down custom build hardware
–Use strong KDF to derive keys (PBKDF2®Argon2)
•Use password-authenticated key exchange instead of password check
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PV204 Authentication and passwords
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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Handling passwords in source code
•Limiting memory exposure
–Load only when needed
–Erase right after use
–Pass by reference / pointer to prevent copy in memory
–Derive session keys
•Don’t hardcode password into application binary
•Nice presentation (K. Kohli, examples how NOT to):
http://www.slideshare.net/amiable_indian/insecure-implementation-of-security-best-practices-of-hash
ing-captchas-and-caching-presentation
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PV204 Authentication and passwords
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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Hard-coded password might be visible both in application binary and memory
PV204 Authentication and passwords
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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Alternative to hardcoded passwords/keys
•Don’t use passwords J
•Ask the user for a password
•Keep secrets in a separate file
•Encrypt stored secrets
•Store secrets in protected database
•Use already existing authentication credentials
•CERN guidelines
–https://security.web.cern.ch/security/recommendations/en/password_alternatives.shtml
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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Group activity
•Form group of 3-4 members (mix, not your neighbours)
–Introduce yourself with your name
•Discuss and write down on paper:
–What method(s) you use for authentication (password…)
–Is server using other authentication factor?
–How you store the authentication secret? (brain-only…)
•Time limit: 5 minutes
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•Now return back to your original seat (if you wish J)
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          https://crocs.fi.muni.cz  @CRoCS_MUNI
Activity:
•Think about one or two surprising things from this lecture
•
•I want to hear at least 5 of these, tell me please J
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